Former Tropical Depression Ten strengthened to Tropical Storm Idalia over the Northwestern Caribbean Sea east of the Yucatan Peninsula on Sunday morning. At 11:00 a.m. EDT on Sunday the center of Tropical Storm Idalia was located at latitude 19.9°N and longitude 85.8°W which put it about 80 miles (130 km) east-southeast of Cozumel. Idalia was moving toward the east at 2 m.p.h. (3 km/h). The maximum sustained wind speed was 40 m.p.h. (60 km/h) and there were wind gusts to 50 m.p.h. (80 km/h). The minimum surface pressure was 1001 mb.

A Tropical Storm Warning was in effect for the portion of the coast from Tulum to Rio Lagartos, Mexico. The Tropical Storm Warning included Cozumel. A Tropical Storm Warning was also in effect for the Cuban Province. of Pinar del Rio. A Tropical Storm Watch was in effect for the Isle of Youth.

A NOAA research aircraft found sustained tropical storm force winds in former Tropical Depression Ten on Sunday morning and the U.S. National Hurricane Center upgraded the system to Tropical Storm Idalia. There was a low level center of circulation meandering around inside of a larger counterclockwise rotation over the Northwestern Caribbean Sea. Thunderstorm activity fluctuated near the low level center of circulation. There were few thunderstorms currently near the low level center. There were bands of showers and thunderstorms in the larger counterclockwise circulation. The thunderstorms in the larger circulation generated upper level divergence that pumped mass away from the tropical storm. Winds to tropical storm force extended out 35 miles (50 km) from the low level center of circulation.

Tropical Storm Idalia will be in an environment mostly favorable for intensification during the next 24 hours. The tropical depression will be over water where the Sea Surface Temperatures are near 30°C. It will be under an upper level ridge over the Yucatan Channel. The winds are weak in the upper level ridge and there will be little vertical wind shear. However, much of the air moving around the western side of Tropical Storm Idalia will pass over the northeastern Yucatan Peninsula. Some of the air in the eastern side of the Idalia will pass over western Cuba. The flow of air over land will inhibit intensification, but it probably will not prevent intensification. Tropical Storm Idalia could intensify slowly on Sunday. Idalia could intensify to a hurricane early next week when it moves over the eastern Gulf of Mexico.

Tropical Storm Idalia will be in a region where the steering currents are weak during the next 12 hours. Idalia may not move much during the rest of Sunday. A high pressure system over the western Atlantic Ocean will start to steer Idalia toward the north on Monday. On its anticipated track Tropical Storm Idalia Ten will move over the eastern Gulf of Mexico on Monday.

Tropical Storm Idalia will drop heavy rain over parts of the northeastern Yucatan Peninsula and western Cuba. Heavy rain could cause flash floods in some locations.

Elsewhere, Hurricane Franklin continued to strengthen over the Atlantic Ocean south-southwest of Bermuda. At 11:00 a.m. EDT on Sunday the center of Hurricane Franklin was located at latitude 25.1°N and longitude 69.3°W which put it about 565 miles (905 km) south-southwest of Bermuda. Franklin was moving toward the north-northwest at 8 m.p.h. (13 km/h). The maximum sustained wind speed was 100 m.p.h. (160 km/h) and there were wind gusts to 120 m.p.h. (195 km/h). The minimum surface pressure was 971 mb.